U.S. patent number 6,957,036 [Application Number 10/753,387] was granted by the patent office on 2005-10-18 for fixing member, fixing device, and image forming apparatus.
This patent grant is currently assigned to Ricoh Company, Limited. Invention is credited to Toshihiko Baba, Katsuhiro Echigo, Takashi Fujita, Hisashi Kikuchi, Hiroyuki Kunii, Shigeo Kurotaka, Atsushi Nakafuji, Yukimichi Someya.
United States Patent |
6,957,036 |
Kikuchi , et al. |
October 18, 2005 |
**Please see images for:
( Certificate of Correction ) ** |
Fixing member, fixing device, and image forming apparatus
Abstract
A fixing member heat bonds a toner on a recording material. The
fixing member includes a releasing layer, a layer of elastic
material, below the releasing layer, and a layer of adiabatic and
hygroscopic material, below the layer of elastic material. The
layer of elastic material includes a layer of electrically
conducting material to pass electric currents, an adiabatic,
elastic, and hydrophobic material, and a porous material to the
release of the moisture absorbed by the layer of adiabatic and
hygroscopic material.
Inventors: |
Kikuchi; Hisashi (Kanagawa,
JP), Baba; Toshihiko (Chiba, JP), Kurotaka;
Shigeo (Kanagawa, JP), Nakafuji; Atsushi (Tokyo,
JP), Kunii; Hiroyuki (Kanagawa, JP),
Someya; Yukimichi (Saitama, JP), Echigo;
Katsuhiro (Saitama, JP), Fujita; Takashi
(Kanagawa, JP) |
Assignee: |
Ricoh Company, Limited (Tokyo,
JP)
|
Family
ID: |
32895270 |
Appl.
No.: |
10/753,387 |
Filed: |
January 9, 2004 |
Foreign Application Priority Data
|
|
|
|
|
Jan 10, 2003 [JP] |
|
|
2003-004238 |
|
Current U.S.
Class: |
399/333;
399/329 |
Current CPC
Class: |
G03G
15/2057 (20130101); G03G 2215/2048 (20130101); Y10T
428/249933 (20150401) |
Current International
Class: |
F16C
13/00 (20060101); G03G 15/20 (20060101); G03G
015/20 () |
Field of
Search: |
;219/216,619
;399/320,328,329,330,333 ;430/99,124 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
2000-242108 |
|
Sep 2000 |
|
JP |
|
2001-201966 |
|
Jul 2001 |
|
JP |
|
2002-334774 |
|
Nov 2002 |
|
JP |
|
Primary Examiner: Ngo; Hoang
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier
& Neustadt, P.C.
Claims
What is claimed is:
1. A fixing member that heat bonds a toner on a recording material
by heating, comprising: a releasing layer, a layer of elastic
material, below the releasing layer, and a layer of adiabatic and
hygroscopic material, below the layer of elastic material, wherein
the layer of elastic material includes a layer of electrically
conducting material to pass electric currents, an adiabatic,
elastic, and hydrophobic material, and a porous material to the
release of the moisture absorbed by the layer of adiabatic and
hygroscopic material.
2. The fixing member according to claim 1, wherein the porous
material is made of a plurality of hollow fibers made of a
hygroscopic heat-resistant material and the adiabatic, elastic, and
hydrophobic material is a binder, and the layer of electrically
conducting material is disposed around the hollow fibers.
3. The fixing member according to claim 1, wherein the porous
material of the layer of elastic material is deposed on the layer
of adiabatic and hygroscopic material such that there are empty
spaces between the porous material and the layer of adiabatic and
hygroscopic material, and the layer of electrically conducting
material is disposed on the porous material.
4. The fixing member according to claim 1, wherein the layer of
electrically conducting material is chemically coupled with at
least one of the layers adjoining the conductive layer.
5. The fixing member according to claim 1, comprising as a single
unit a primary coil and a secondary coil that is magnetically
coupled with the primary coil, wherein induction current produced
by the secondary coil flows through the layer of electrically
conducting material.
6. A fixing member that heat bonds a toner on a recording material
by heating, comprising: a releasing layer; a first layer of
adiabatic and hydrophobic material, below the releasing layer; a
layer of electrically conducting material, below the first layer,
to pass electric currents; and a second layer of adiabatic and
hydrophobic material, below the layer of electrically conducting
material, wherein at least one of the first layer and the second
layer is made of elastic material.
7. The fixing member according to claim 6, wherein the releasing
layer is made of a fluorocarbon resin and the second layer is made
of rubber.
8. The fixing member according to claim 6, wherein the first layer
and the second layer are made of rubber, and a deformation of the
first layer and the second layer is 10% or less.
9. The fixing member according to claim 6, wherein the layer of
electrically conducting material is chemically coupled with at
least one of the layers adjoining the conductive layer.
10. The fixing member according to claim 6, comprising as a single
unit a primary coil and a secondary coil that is magnetically
coupled with the primary coil, wherein induction current produced
by the secondary coil flows through the layer of electrically
conducting material.
11. A fixing device comprising a fixing member and a pressure
member made of an air-containing adiabatic material, wherein the
fixing member heat bonds a toner on a recording material by heating
and includes a releasing layer, a layer of elastic material, below
the releasing layer, and a layer of adiabatic and hygroscopic
material, below the layer of elastic material, wherein the layer of
elastic material includes a layer of electrically conducting
material to pass electric currents, an adiabatic, elastic, and
hydrophobic material, and a porous material to the release of the
moisture absorbed by the layer of adiabatic and hygroscopic
material.
12. A fixing device comprising a fixing member and a pressure
member made of an air-containing adiabatic material, wherein the
fixing member heat bonds a toner on a recording material by heating
and includes a releasing layer; a first layer of adiabatic and
hydrophobic material, below the releasing layer; a layer of
electrically conducting material, below the first layer, to pass
electric currents; and a second layer of adiabatic and hydrophobic
material, below the layer of electrically conducting material,
wherein at least one of the first layer and the second layer is
made of elastic material.
13. An image forming apparatus comprising a fixing member that heat
bonds a toner on a recording material by heating, the fixing member
includes a releasing layer, a layer of elastic material, below the
releasing layer, and a layer of adiabatic and hygroscopic material,
below the layer of elastic material, wherein the layer of elastic
material includes a layer of electrically conducting material to
pass electric currents, an adiabatic, elastic, and hydrophobic
material, and a porous material to the release of the moisture
absorbed by the layer of adiabatic and hygroscopic material.
14. An image forming apparatus comprising a fixing member that heat
bonds a toner on a recording material by heating, the fixing member
includes a releasing layer; a first layer of adiabatic and
hydrophobic material, below the releasing layer; a layer of
electrically conducting material, below the first layer, to pass
electric currents; and a second layer of adiabatic and hydrophobic
material, below the layer of electrically conducting material,
wherein at least one of the first layer and the second layer is
made of elastic material.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
The present document incorporates by reference the entire contents
of Japanese priority document, 2003-004238 filed in Japan on Jan.
10, 2003.
BACKGROUND OF THE INVENTION
1) Field of the Invention
The present invention relates to a fixing member that employs an
electro magnetic induction heating to fix an image to a recording
member.
2) Description of the Related Art
An image forming apparatus that employs a toner in order to form a
visible image is provided with a fixing device to fix a toner image
on a recording material. Different approaches are used to perform
the fixing: apply heat and/or pressure to the toner image, use a
solvent and the like. However, application of heat or pressure has
been the most popular method. A fixing device that applies heat
(hereinafter, "heat fixing method") includes a fixing roller and a
pressure member that is in pressure contact with the fixing roller.
The fixing roller is heated and then the recording material that
bears the toner image is passed between the fixing roller and the
pressure member. As a result, the toner image is fixed on the
recording material. In a variation, the toner image is transferred
from an intermediate transfer drum on to a fixing member and then
the toner image on the fixing member is fixed to the toner image on
the recording material.
However, in the heat fixing method, the conversion of energy is
inefficient, the power consumption is high, and the warming up time
is long. To overcome these problems, eddy currents heating method
and induction heating method came to be used. In the eddy currents
heating method the fixing roller is heated by the eddy currents due
to the electromagnetic waves, while in the induction heating
method, a fixing roller that is formed from a metal conductor is
heated by energizing a heating element. These direct heating
methods proved highly efficient; because, the heating time is very
less. These heating methods also gained popularity since the
rigidity of the fixing roller was not affected by the heat.
Many patents related to the direct heating methods have been
disclosed, some of which are mentioned below. See, for example,
Japanese Patent Laid-Open Publication No. 2000-242108.In the
technology disclosed in this publication, a heating belt is placed
opposite to an electromagnetic induction heating device. The
heating belt includes a heat-resistant resin or rubber base on
which is disposed an organic conductive layer having the property
of heating by electromagnetic induction and which gets heated by an
eddy current loss. Alternatively, the heating belt may include a
non-woven fiber base and on which is disposed a conductive layer
having the property of being heated by electromagnetic induction
and which gets heated by an eddy current loss.
Japanese Patent Laid-Open Publication No. 2002-334774 also
discloses a related technology. In the technology disclosed in this
publication, a fixing member is equipped with a high frequency
source HFS that outputs high frequency of over 100 kHz, an
induction coil IC biased by the high frequency output of the high
frequency source HFS, and a fixing roller HR. The fixing roller HR
has a conductive layer of a thickness less than that of the skin,
and the conductive layer gets heated by the secondary current
flowing in the induction coil IC in the circumferential
direction.
In the fixing member employing direct heating method, it is
required that the layers of the fixing member are in tight contact.
Otherwise, heat conduction is not uniform and efficient and
problems such as unevenness of temperature, reduced resistance to
pressure, etc. may arise. Particularly, in a high-temperature and
high-moisture environment (for instance a temperature of 30 degrees
and humidity of 70%) such as during the rainy season of the
inventor's country, if moisture absorption in a layer exceeds 0.07
mg/cm.sup.2, during heating a sharp expansion takes place due to
evaporation and as a result the conductive layer peels off.
A solution for such a problem is provided in Japanese Patent
Laid-Open Publication No. 2001-201966.This publication discloses a
heat generating roller in which is provided a resistive element
through an insulation on the inner perimeter of the base material.
This forms a bump on the inner perimeter of the base material. The
concave portion and the opening in the insulation layer for
ventilation open to the outside. However, since the heat producing
part is separated from the surface layer, the rise time is somewhat
longish for a direct heating method.
In recent times, the popularity of color image forming apparatuses
is on the increase. There is a demand for realizing high-quality
pictures by realizing a fixing member with a surface which is
flexible enough to allow toners of multiple colors to be uniformly
transferred to a recording material by pressure.
However, in the structure described in Japanese Patent Laid-Open
Publication No. 2001-201966, the inner perimeter of the metal base
has plural layers such as heat-producing layer (conductive layer),
etc. This adversely affects the flexibility of the surface of the
heating roller. Further, for the regular high frequency of 20
kilohertz (kHz) to 100 kHz used in the electromagnetic induction in
the structure disclosed in patent literature 1, the thickness
organic conduction layer (skin thickness) should preferably be 1
micrometer (.mu.m) to 50 .mu.m. The conductive layer which has a
thickness of this range is bound to have poor flexibility.
SUMMARY OF THE INVENTION
It is an object of the present invention to solve at least the
problems in the conventional technology.
A fixing member according to one aspect of the present invention
heat bonds a toner on a recording material by heating and includes
a releasing layer, a layer of elastic material, below the releasing
layer, and a layer of adiabatic and hygroscopic material, below the
layer of elastic material. The layer of elastic material includes a
layer of electrically conducting material to pass electric
currents, an adiabatic, elastic, and hydrophobic material, and a
porous material to the release of the moisture absorbed by the
layer of adiabatic and hygroscopic material.
A fixing member according to one aspect of the present invention
heat bonds a toner on a recording material by heating and includes
a releasing layer; a first layer of adiabatic and hydrophobic
material, below the releasing layer; a layer of electrically
conducting material, below the first layer, to pass electric
currents; and a second layer of adiabatic and hydrophobic material,
below the layer of electrically conducting material, wherein at
least one of the first layer and the second layer is made of
elastic material.
A fixing device and an image forming apparatus according to other
aspects of the present invention employ the fixing member according
to the present invention.
The other objects, features, and advantages of the present
invention are specifically set forth in or will become apparent
from the following detailed descriptions of the invention when read
in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an overall view of an image forming apparatus according
to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a fixing device according to an
embodiment of the present invention;
FIG. 3A is a cross-sectional view perpendicular to a rotational
axis of a fixing roller of the fixing device;
FIG. 3B is a cross-sectional view parallel to the rotational axis
of the fixing roller;
FIG. 4 is an example of a structure of a fixing member;
FIG. 5 is another example of a structure of the fixing member;
FIG. 6 is still another example of another fixing member;
FIG. 7 is still another example of another fixing member;
FIG. 8 is still another example of another fixing member;
FIG. 9 is an example of a structure of a fixing member used for
comparison;
FIG. 11A through FIG. 11J are conceptual drawings of various
magnetic circuit structures;
FIG. 12A and FIG. 12B illustrate an example of a coil which is made
by winding a thin wire over a base material that is rolled such
that the front and the backside of the base material overlap.
FIG. 13 is a conceptual drawing of a belt shaped fixing member.
DETAILED DESCRIPTION
Exemplary embodiments of a fixing member, a fixing device, and an
image forming apparatus according to the present invention are
explained in detail next with reference to the accompanying
drawings. FIG. 1 illustrates a digital color printer employing a
tandem system to which the present invention is applicable. The
overall structure of the image forming apparatus is identical to
the conventional image forming apparatus.
This color printer includes an assembly of an image scanner, an
automatic document feeder (ADF), a sorter, and other devices (the
color printer being essentially a multi-function digital color
copier). An image scanner has been omitted for the sake of
simplification of the explanation. The color printer comprises four
image-creating units along the edge of a transfer belt 10 of a
conveying belt unit. The image-creating unit creates a toner image
of each of the four colors, namely, yellow, magenta, cyan, and
black (In the figures, the four colors are represented by a, b, c,
and d, respectively). The transfer belt is an endless belt that is
supported by a driving roller 9, a tension roller 13a, and a driven
roller 13b.The tension of the transfer belt 10 is maintained almost
uniformly as the tension roller 13a pushes down the transfer belt
10 with a not shown spring.
Each image-creating unit has an image carrier in the form of a
photosensitive drum 6. When an image data of each color is sent to
a writing unit (multi-beam writing) 5, the photosensitive drum 6 is
rotated in the counter-clockwise direction by a not shown driving
device, and a laser beam exposes the image data unit by unit in
accordance with the image data on the photosensitive body 6 which
is uniformed charged by a charging unit. A latent image is formed
on the photosensitive body 6 due to this exposure. A developing
unit 7 develops this latent image into a toner image. The toner
image then is transferred to a position that faces the transfer
belt 10.
Meanwhile, a paper feeder 8 feeds a sheet. The sheet is carried by
a resist roller on the transfer belt 10 at the same time as the
toner image. A transferring unit 11 transfers the toner image to
the sheet.
In a full color printing process, while a yellow toner image formed
in the first image-creating unit is being transferred to the sheet,
a latent image of magenta color is formed on the second
image-creating unit and upon development of the latent image by the
developing unit 7 into a magenta toner image, the magenta toner
image is transferred to the sheet, thus obtaining a magenta toner
image superposed on the yellow toner image. Similarly, a cyan toner
image and a black toner image are formed and superposed on the
sheet. The sheet containing the superposed toner images of the four
colors is detached from the transfer belt 10 and carried to a
fixing unit 12. A cleaning unit removes the residual toner after
transfer of the toner image on each of the photosensitive bodies,
readying the photosensitive bodies for the next round of image
formation process.
FIG. 2 is a detailed drawing of the fixing unit 12. A fixing roller
23 is in pressure contact with a pressure roller 22 because of a
pressure spring 20 and a pressure arm 21. The fixing roller 23
rotates in clockwise direction. The sheet having the unfixed toner
images is held between the fixing roller 23 and the pressure roller
22 and is transferred towards left in the drawing. An oil-coated
roller 24, a thermistor 25, a temperature fuse 26, and a separating
nail 27 are disposed around the fixing roller 23. A paper guide
plate 28 is disposed opposed to the nip formed by the pressure
roller 22 and the fixing roller 23. A discharge guide plate 29 is
disposed opposed to the nip, on the other side of the paper guide
plate 28, and ejects the sheet after fixing is completed. The
pressure roller 22 may for instance be a sponge roller.
FIG. 3A is a cross-sectional view perpendicular to a rotational
axis of the fixing roller 23, and FIG. 3B is cross-sectional view
parallel to the rotational axis. The outermost layer is a releasing
layer 30. Beneath the releasing layer 30 are an intermediate
elastic layer 31 and an adiabatic layer 38. The intermediate
elastic layer 31 and the adiabatic layer 38 are supported by a base
39. The base 31 is insulating and is made of, for example, glass.
The intermediate elastic layer 31 includes a conductive layer which
is electrically connected to a secondary coil 41 on the base 39
side through a connector 40. The center of the fixing roller 23 has
a core 42 around which a primary coil 43 is wound. The
electromagnetic induction between the primary coil 43 and the
secondary coil 41 generates heat in the conductive layer.
FIG. 4 through FIG. 8 illustrate the detailed structure of the
intermediate elastic layer 31. In order to make the explanation of
the features of this layer clearer, FIG. 9 and FIG. 10 are provided
as examples for comparison. The adiabatic layer 38 is about 1 .mu.m
to 5 .mu.m thick and is made of a heat-resistant resin or rubber.
The releasing layer 30 is about 10 .mu.m to 30 .mu.m and is made of
fluorocarbon resin such as PFA resin. As shown in FIG. 4 and FIG.
5, the intermediate elastic layer 31 may be include hollow fibers
32 having an outer diameter of 50 .mu.m to 300 .mu.m and an inner
diameter of 40 .mu.m to 290 .mu.m and each of the hollow fibers 32
having an external cladding of a conductive layer 33. The hollow
fibers 32 are disposed parallel to each other and are bound
together as a single unit by a binder in the form of a hydrophobic
heat-resistant rubber 34. The hollow fiber 32 is made of a
hygroscopic heat-resistant material such as polyester, polyimide,
polyamide-imide, polybenzoimidazole. As shown in FIG. 4, each of
the hollow fibers 32 may have separate conductive layer 33, or as
shown in FIG. 5, the hollow fibers 32 may have a common conductive
layer 33. There may be two or more layers of the hollow fibers.
When there are many layers of the hollow fibers, and if a
conducting layer is not provided in the bottom-most layer, this
layer may function as an adiabatic layer.
In the structures illustrated in FIG. 6 through FIG. 8, the
conductive layer 33 is invested with the function of a sheet
heating member that uses induction current. In FIG. 6, the
conductive layer 33 is sandwiched the heat-resistant rubber layer
32 that ensures surface flexibility, and the base material 32 that
is made of a hygroscopic material, such as polyimide, etc., so as
to generate space for moisture elimination. The surface of the
polyimide base material 36 on the side opposite to the one that has
the conductive layer 33 has a bump (20 .mu.m to 200 .mu.m in
height, and 20 .mu.m to 50 .mu.m in width) and is in close contact
with the adiabatic layer 38 beneath it. In the structure
illustrated in FIG. 7, the conductive layer 33 is disposed beneath
the releasing layer 30. The heat-resistant rubber layer 35 is
disposed beneath the conductive layer 33. In the structure
illustrated in FIG. 8, the conductive layer 33 is disposed between
two heat-resistant rubber layers 35 and 35' beneath the releasing
layer 30. In FIG. 9, which is provided for comparison, solid
hygroscopic heat-resistant fibers are used instead of hollow
fibers. In FIG. 10, the hygroscopic base material does not have a
bump.
The conductive layer 33 is formed by conductive macromolecule
material obtained by polymerization of pyrrol or its derivatives.
Copper sulfuration is a well-known metal sulfuration process.
Copper sulfuration is a process by which sulfurated copper is
chemically bonded to the surface of a resin base material. To
explain the chemical binding in further detail, binding of
sulfurated copper to the resin typically involves interaction
between an ion of the resin whose surface has a functional group
that can capture a metal ion and an aqueous bath that includes a
thiosulphate ion. Thunderon, manufactured by Nihon Sanmo Dyeing
Co., is a typical industrial product obtained by processing the
surface of a base material such as a fiber with sulfurated
copper.
Pyrrol, N-methyl pyrrol, aniline, thiophane, thiophase-3-sulfonic
acid or a polymer or copolymer obtained by polymerizing these
monomer conductive materials can be used as conductive
macromolecule materials. ST-poly, manufactured by Achilles
Corporation, is a typical industrial product formed from
polypyrrol. Conductive organic polymers of monomers such as Pyrrol
and thiophane are preferable from the point of view of contact
strength, conductivity, and ease of processing of the conductive
layer 33. When cladding the surface of the fiber with the
conductive polymer (or when impregnating the fiber with the
conductive polymer), the layer thickness is kept between 0.02 .mu.m
to 0.05 .mu.m bearing in mind the heat resistivity. The thickness
of the conductive layer 33 of the conductive polymer varies with
the diffusion conditions of the processing liquid used during the
conductivity process. When polymerization is carried out using
oxygenated polymerization agent as a catalyst by submerging the
base fiber in the processing fluid, the conductive polymer thus
generated either adheres to the surface of the fiber or forms a
cladding on the surface or infiltrates into the fiber material.
Thus, the conductive organic polymer and the base fiber together
form the conductive layer 33. Either water or a mixture of water
and organic solvent can be used as the processing fluid, also known
as a solvent of the polymerization system, depending on the surface
conditions of the base material and the diffusion conditions.
Copper sulfurization process is another well-known conductivity
process. In this process, sulfurated copper is cladded on the
surface of the base material according to sufurated copper plating
method. Other methods include cladding metals such as nickel,
aluminium, etc. According to electroless metal plating method,
binding with a binding agent a metal foil or a thin sheet of metal
on the organic conductive layer, etc. However, electro plating or
chemical plating is preferable from the viewpoint of obtaining a
metal layer of uniform thickness over the organic conductive layer.
For instance, a phosphorous eutectoid plating such as Ni--P, Fe--P
plating can be obtained by adding a phosphate compound while
bathing the base material. Similarly, a carbon eutectoid plating
such as Ni--C, Fe--C plating can be obtained by adding a
carboxylate compound. Alternatively, a boron eutectoid plating such
as Ni--B, Fe--B plating can be obtained by adding boron compounds.
Particularly, when metal-plating the organic conductive layer, it
is preferable to first chemically etch the surface, then form a
thin alloy plating layer by phosphorous plating, carbon plating or
boron plating, and finally form a metal layer of desired thickness
over the thin alloy plating layer by electro plating or chemical
plating. The plating layer can be firmly bound on the surface by
the above method. Instead of plating process, the metal layer may
also be formed by vacuum deposition, sputtering, etc. These methods
may be employed for metals which do not yield themselves to
plating.
Upon placing the fixing rollers having the structures illustrated
in FIG. 4 through FIG. 10 under an environment mimicking the rainy
season, that is, at an average temperature of 30.degree. C. and a
relative humidity of 70%, it was noted that in the structures
according to FIG. 9 and FIG. 10 the conductive layer pealed off due
to the moisture, whereas in the structures according to FIG. 4
through FIG. 8, the conductive layer remained intact.
When the conductive layer is formed within the releasing layer 30
made of fluorocarbon resin, as shown in FIG. 7, the adhesion is not
very good. However, the adhesion can be improved by laying the
conductive layer after laying a thin layer of primer on the
releasing layer side of the heat-resistant rubber layer 35. The
primer layer is hard and may be hygroscopic. Therefore the
thickness of the primer layer should be kept between 0.5 .mu.m to 2
.mu.m so that it does not affect the flexibility of the surface. If
a tube of fluorocarbon resin is used as a releasing layer, the
fluorocarbon from the inner surface of the tube should be desorbed
by conventional methods such as laser ablation, ammonia process,
natrium naphthalene process, etc. and the exposed layer should be
chemically activated followed by laying of the conductive layer and
then the primer layer to establish contact with the adiabatic
layer, etc. Laser ablation is a preferable mode of desorption since
in the other methods desorption process involves using fluid and
the subsequent filtering out of the fluid which result in creases
and folds in the tube. Laser ablation is particularly preferred for
obtaining good quality images in image forming apparatuses of
resolution of over 600 dpi.
When the conductive layer is disposed between two heat-resistant
rubber layers, as shown in FIG. 8, the durability of the conductive
layer is good irrespective of the process used for laying the
conductive layer, as long as the deformation amount of the portion
of the heat-resistant layer which includes the conductive layer is
within 10% of the result obtained by the finite element method.
FIG. 11A through FIG. 11J illustrate various structures of magnetic
circuits. The magnetic circuit is formed by placing appropriately a
highly magnetically permeable and a high resistance material such
as soft ferrite. The heat-producing efficiency of the conductive
layer can be increased by forming the magnetic circuit.
FIG. 11A, a yoke is provided external to the fixing member in the
structure illustrated in FIG. 3. In the structure illustrated in
FIG. 11B, the primary coil wound around the core is fixed inside
the fixing member and the electromagnetic induction current is
directly induced in the conductive layer instead of being produced
in the secondary coil. When the frequency exceeds 500 kHz, the
coupling factor of the electromagnetic coupling increases. Hence,
the core can be dispensed with in all the cases except in the
structure illustrated in 11A. FIG. 11C illustrates a structure in
which a yoke is placed external to the structure shown in FIG. 11B.
The opening of the fixing member can be heated in a concentrated
manner as the lines of magnetic force are concentrated on the yoke
side.
In the structure illustrated in FIG. 11D, the core with the coil
wound around it is placed external to the fixing member and the
yoke is placed inside the fixing member. The lines of magnetic
force due to the core and the yoke are concentrated near the
conductive layer. In the structure illustrated in FIG. 11E, the
direction of winding of the coil and the shape of the yoke are
different from those shown in FIG. 11D. In the structure
illustrated in FIG. 11F, the internal yoke shown in FIG. 11D is
downscaled to a required size. In the structure illustrated in FIG.
11G, the internal yoke shown in FIG. 11E is downscaled to a
required size. In the structure illustrated in FIG. 11H, the center
is occupied by a non-magnetic metal around which a ferrite layer or
a layer of ferrite hardened with heat resistant resin or ceramic is
disposed. The ferrite layer controls lines of magnetic force does
not allow the central metal to get heated. In the structure
illustrated in FIG. 11I, the direction of winding of the coil and
the shape of the yoke are different from those shown in FIG.
11H.
In the structures shown in FIG. 11A through 11I, only a single
conductive layer has been depicted. It is advantageous from the
viewpoint of flexibility to have a thin conductive layer if it is
close to the surface. However, it is also possible to have a
double-conductive layer structure by having a first conductive
layer close to the surface and a second conductive layer a little
away from the surface. In this structure, the heating rate of the
first conductive layer can be reduced. FIG. 11J illustrates such a
structure. A conventionally known material that is somewhat
inferior in terms of flexibility such as a metal foil can be used
as the second conductive layer.
Simplification of induction coil in a fixing device employing
induction heating has been a constant challenge. Litz wire may be
used as the induction coil. Alternatively, as shown in FIG. 12A, a
lightweight coil obtained by rolling up a flexible polyimide board
and winding thin wires around it so that the ends of the wires
connect (1 connects with 1, 2 with 2, and so on) at the overlapping
portion of the flexible board.
For the structures illustrated in FIG. 11E, FIG. 11G, and FIG. 11I,
a single layer or plural layer of coil may be wound around the base
material and a coil may be formed by assembling the
coil-around-base material with a core. In particular, coil having a
special shape, parallel coil, etc. are ideal. When the thin wires
are placed in parallel, the surface area of the thin wire increases
and a high-frequency current can be obtained as in the litz wire.
This coil is not restricted to the fixing member described in
claims 1 through 7 and can be used for induction heating of any
kind.
The layer structure and the conductivity process have been
described above for the intermediate elastic layer disposed between
the adiabatic layer and the releasing layer of the fixing roller.
These are also applicable to the intermediate elastic layer of a
fixing belt. In the case of the fixing belt, the belt lies where
the adiabatic layer should be and the thickness of the belt ranges
from 30 .mu.m to 100 .mu.m. FIG. 13 is a drawing illustrating a
belt-type fixing member according to the present invention. If the
belt base material is a very thin polyimide board of a thickness of
50 .mu.m or less, the amount of moisture absorbed will be
negligible and the moisture is likely to drain from the bottom
surface of the belt. If the belt is as thin as 30 .mu.m, durability
under the existing conditions may be compromised.
Along with heating of the conductive layer according to the present
invention, other heating methods such as using another
heat-producing layer, or using alternative heating methods such as
by radiation, etc., may also be effectively used.
According to one aspect of the present invention, the conductive
layer can be prevented from peeling off due to absorption of
moisture. Further, the conductive layer is insulated by the space.
The heat is therefore shunted towards the surface. Consequently,
the heating rate close to the surface improves.
When the conductive layer is disposed exterior to a hollow fiber,
and a heat-resistant rubber is used as a binder, the fiber itself
is rendered flexible. Further, using a thin rubber layer helps
obtain high quality image. The hollow fiber allows continuous
conduction and is easy to manufacture.
When the conductive layer is disposed on the outer periphery of a
cylindrical base material and a bump is disposed on the inner
periphery of the cylindrical base material, and the space for the
release of the moisture is formed by the convex part of the bump
touching an adjoining layer, an even conductive layer and therefore
an even heating is obtained, as compared to when the conductive
layer is disposed on the surface of the fiber.
The conductive layer has an elastic hydrophobic heat-resistant
material on its surface, a hygroscopic heat-resistant material on
its underside, and space on the side of the underside of the
conductive layer for the release of the moisture absorbed by the
hygroscopic heat-resistant material. Consequently, the conductive
layer can be prevented from peeling off due to absorption of
moisture.
When the conductive layer is between two heat-resistant rubber
layers and the deformation of the rubber layers is 10% or less,
even if the outermost releasing layer gets damaged, there is a very
low possibility of the heat-producing conductive layer to be
affected. Further, the conductive layer is unaffected by the
deformation of the rubber layers.
When the conductive layer is chemically coupled with at least one
of the layers adjoining it, the strong coupling ensures that the
conductive layer does not peel off even upon bending. A thin
conductive layer with excellent flexibility can be heated by an
induction current produced in a secondary coil in a structure in
which the secondary coil is magnetically coupled with a primary
coil and the primary coil and the secondary coil exist as a single
unit.
Although the invention has been described with respect to a
specific embodiment for a complete and clear disclosure, the
appended claims are not to be thus limited but are to be construed
as embodying all modifications and alternative constructions that
may occur to one skilled in the art which fairly fall within the
basic teaching herein set forth.
* * * * *